Motion is still an unsolved problem in Magnetic Resonance Imaging (MRI), as well as other imaging modalities, and is a dominant source of artifacts. Motion can result in prolonged or diagnostically inadequate studies. This can lead to considerably lower diagnostic confidence or even incorrect diagnoses. To overcome motion in some cases requires the use of sedation or general anesthesia, which can add extra risk factors to a diagnostic patient work-up. Moreover, the decreased patient comfort and through-put is inconvenient for both the patient and the clinicians, and can add significantly to overall exam/health care costs. Providing an accurate and reliable marker for 3D motion tracking is key for many prospective or retrospective motion correction approaches.
Using two or more cameras, the position of a 3D marker in space can be determined via epipolar geometry. Similarly, a single camera can be used to determine the position of a marker of known geometry. A limitation of these approaches is that the pose estimation fails if only part of the marker is visible, such as in case of large pose changes or when the view to the marker is partially obstructed. Furthermore, the image quality (lens distortion, focus) has to be similar across the entire field of view (FOV), or for all positions in 3D space where the marker is placed. For large motion or large camera apertures, this can become problematic and both precision and accuracy of pose estimation can be considerably impaired.